Nd Model Age Mapping of the Central Gneiss Belt In the western Grenville Province of Ontario, Canada.
Notice bibliographique
Résumé
Nd isotope analysis is well suited for mapping major tectonic boundaries in highly metamorphosed orogenic belts. In this study, approximately 80 samples have been analyzed to map 2 such boundaries in the Central Gneiss Belt of the Grenville Province of Ontario. In Central Ontario, lithotectonic terranes with mapped outcrops of gneisses intruded by eclogites and/or coronitic metagabbro have Nd model ages less than 1.8 Ga are interpreted as components of the allochthonous polycylic belt. More northerly terranes are comprised of similar gneissic materials, but have different types of mafic intrusives and have model ages greater than 1. 8 Ga. These terranes are interpreted as fragments of the parautochthonous belt. These two belts are divided by a major thrust, termed the Allochthon Boundary Thrust (ABT) (Rivers, et. al., 1989). Continuing to the north, another step in the Nd model ages has been used to identify and map a cryptic suture between Archean and early Proterozoic crustal materials (Dickin & McNutt, 1989). Along the Georgian Bay coastline, between Pointe Au Baril and Parry Sound, the Shawanaga Shear Zone has been interpreted as the location of the ABT (Culshaw, et. al., 1994). Analysis of over 50 samples are used to map the crustal formation ages in this region and have confirmed this interpretation. Orthogneisses of the Britt Domain have Nd model ages in the range 1.8- 1.9 Ga. Reworking of the original crust has given these rocks U-Pb crystallization ages of~ 1.45 Ga, which means that these rocks have been metamorphosed prior to the Grenvillian event. Crossing the ABT, the orthogneisses of the Shawanaga Domain have a younger range of crustal formation ages, 1.4 - 1.7 Ga. The U-Pb crystallization ages of these rocks are ~ 1.36 Ga, and they lack signs pre-Grenvillian metamorphism. To the south of Franklin Island, the location of the ABT is difficult to map, as outcrop lies beneath the waters of Georgian Bay. Results of the Nd isotope analyses suggest that the ABT passes through the western edge of the Snake Islands, rather than to their east, as previously interpreted (Culshaw, et. al., 1994). Approximately 15 Nd isotope analyses were used to investigate a recently proposed location of the ABT (Ketchum & Davidson, 2000) in the vicinity of the Powassan Batholith. Results from near Arnstein, Restoule and Magnetewan agreed with the existing location of the ABT. To the east of the Powassan Batholith, 3 Nd model ages coupled with a lack of mappable eclogites and/or coronitic metagabbros suggest that earlier interpretations of the position of the ABT may be correct and that further studies in this region are necessary. A cryptic suture identified by crustal formation ages has been the focus of several previous studies (Dickin & McNutt, 1989, 1990; Holmden & Dickin, 1995; Dickin, 1998; Guo & Dickin, 1996). This suture has been mapped from the Georgian Bay coast through Lake Nipissing to the Ontario-Quebec border. New Nd isotope analyses and studies of the regional magnetics have identified a thrust slice between the Grenville Front tectonic zone (GFTZ) and the parautochthonous belt. The cryptic suture appears to coincide with a previously undescribed tectonic boundary west of the Key River. To the west of this boundary, straight orthogneisses within the thrust slice have Nd model ages greater than 2.2 Ga. These differ from the orthogneisses and metaplutonic tonalites to the east of this boundary, which exhibit kilometer-scale isoclinal folds and crustal formation ages between 1.8- 2.0 Ga, the previously identified range for the Britt Domain. Major steps in the depleted mantle model ages are observed in all three regions, allowing mapping of the ABT and the Penokean Suture. It is concluded that, in metamorphic orogenic belts, such as the Grenville Province, detailed mapping of major tectonic boundaries is greatly enhanced by the use of Nd isotope analysis.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,002 | 0,002 |
| Études des sciences et des technologies | 0,001 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».